Apertures and Image Stabilization - Queries

[pixelsensor]

Recently bought a D90. I am new to dslr photography although I have used prosumer cameras. So this query may sound funny to some of you. Please bear with me.

Query No. 1 - Apertures
I see lenses have different apertures and focal lengths and they are from many brands too. So if I take a 200-400mm zoom Nikkor and select 300 mm focal length for my shot. I set aperture to say f8. And shoot a scene at 1/200 sec.

Next I shoot the same scene with a say Sigma 150-500mm lens but keep focal length same (300mm) and aperture/shutterspeed too (fixed at f8 - 1/200). Camera is same of course. The scene could be a still life in artificial light (so that the lighting remains unchanged)

Will there be any difference in overall brightness of the two shots? I am not talking quality/sharpness here. Is the aperture scale standardized so that f8 on any lens means a fixed quantity of light?

Query No. 2 - Image Stabilization

VR allows us to shoot 3/4 stops down they say. If I use aperture priority and shoot the same scene twice, once with VR on and then with VR off. All other aspects remain same (focal length, lighting etc.) Will the camera select lower shutterspeed in VR-On mode?

Please enlighten me.

[natek313]

Originally Posted by pixelsensor

Will there be any difference in overall brightness of the two shots? I am not talking quality/sharpness here. Is the aperture scale standardized so that f8 on any lens means a fixed quantity of light?

There shouldn't be any major difference in brightness. You may see color reproduction and saturation differences, but that would be because of the different lenses.

Originally Posted by pixelsensor

VR allows us to shoot 3/4 stops down they say. If I use aperture priority and shoot the same scene twice, once with VR on and then with VR off. All other aspects remain same (focal length, lighting etc.) Will the camera select lower shutterspeed in VR-On mode?

If I understand IS/VR technology (IS: Canon; VR: Nikon), the camera will not automatically select a slower shutter speed with IS/VR turned on. It will meter the scene and select settings just like it would with IS/VR turned off. The IS/VR is only there to help you hand-hold the camera.

Hopefully someone will correct me if I'm wrong.

[sk66]

Nate is right.

Aperture is defined by the opening size in relation to focal length. i.e. a 10mm aperture opening at 40mm focal length = 1/4 or 1:4 or F/4. f/2 means the aperture opening is 1/2 of the focal length.

That is why the aperture number increases (stops down) as you zoom out. The actual opening size is not changing but it's size as a percentage of the focal length is. I.E. a 50mm aperture opening is f/2 (1/2) at 100 mm focal length and will be f/4(1/4) at 200mm.
And, it lets aproximately the same amount of light to the sensor in both cases (there are some losses, but minimal in good lenses).

[pixelsensor]

Thanks Natek & sk66

[das7282]

I agree with the first two responses about aperture.

I also agree with their responses on IS / VR except I would like to clarify a little. All IS or VR does is increases your chances of capturing a sharp image at lower shutter speeds... That's it. The camera does not meter any differently with IS (or VR) turned on vs. turned off.

So for example, most would agree that the minimum shutter speed for hand-held shots (at around 50mm focal length) is around 1/60. But if you're good and stable you might be able to get away with 1/30 sometimes but 1/15 is usually damn near impossible to get a sharp image while hand holding the camera. But if you have a camera or lens with some kind of image stabilization, your chances of getting a sharp image at shutter speeds as low as 1/15 (or lower) are increased.

Also keep in mind that IS or VR does absolutely nothing to prevent image blur caused by a moving subject... It only helps compensate for hand shake.